It is well-known in the art that thermoplastic bottles can be used to contain carbonated liquids for consumer use. For example, soft drinks, sparkling water, beer, etc. are currently packaged in polyethylene terephthalate bottles for distribution and retail sale to the general public.
A problem encountered when using plastic bottles, however, is the loss of carbonation from the packaged beverage over time due to migration of the dissolved carbon dioxide through the bottle wall to the external atmosphere. This loss of carbonation from the beverage, generally referred to as the beverage "going flat", is unacceptable to consumers. In this regard, acceptable carbonation levels for most beverages range from about 2 to about 5 volumes of dissolved carbon dioxide. It is generally agreed that carbonated soft drinks are deemed to be "flat" when the carbon dioxide level drops below about 3.4 volumes of dissolved gas. Regarding the pressure at which the carbonation is maintained within modern plastic bottles, the autogenous pressure may range up to about 100 psi; approximately the highest pressure typically found within a plastic bottle containing a carbonated soft drink.
U.S. Pat. No. 4,342,399 to Stirling discloses a composite bottle, comprising a tubular carbon dioxide-impermeable jacket covering a substantial portion of the body of a carbon dioxide-permeable plastic bottle. This construction is said to reduce the migration of carbon dioxide through the bottle wall, and thus increase the shelf life of the carbonated beverage. The disclosed composite bottle does not, however, reduce the migration of carbon dioxide through those bottle wall portions which are not covered by the impermeable jacket. Moreover, the addition of the impermeable jacket greatly increases the cost, manufacturing complexity, and weight of the resultant composite bottle.
It would be desirable to develop a process for extending the shelf life of a carbonated beverage within a plastic bottle, by reducing the migration of carbon dioxide out through the bottle wall, which process does not comprise modifying the plastic bottle.